In recent years, techniques have been developed which enable simple and rapid image formation by changing the image forming processing for photographic materials using silver halide from the conventional wet process using a developing solution or the like to a dry process using heat application or like means.
Many methods for obtaining color images by heat development have been proposed. For instance, with respect to a method for forming color images by binding couplers to oxidation products of developing agents, there have been proposed combinations of p-phenylenediamine type reducing agents and phenolic or active methylene couplers as described in U.S. Pat. No. 3,531,286, reducing agents of p-aminophenol type as described in U.S. Pat. No. 3,761,270, reducing agents of sulfonamidophenol type in Belgian Pat. No. 802,519 and Research Disclosure, pp. 31-32 (September, 1975), and combinations of sulfonamidophenol type reducing agents with four-equivalent couplers in U.S. Pat. No. 4,021,240.
Further, with respect to a method for forming positive color images using the light-sensitive silver dye bleach process, useful dyes and bleaching methods are described, for example, in Research Disclosure, RD No. 14433, pp. 30-32 (April, 1976), ibid., RD No. 15227, pp. 14-15 (December, 1976), and U.S. Pat. No. 4,235,957.
However, these methods are disadvantageous in that color images obtained are turbid because dye images and silver images or silver salts are coexistent and in that isolated silver is formed during preservation.
In order to overcome the disadvantages described above, a method employing reductive dye providing substances capable of releasing a hydrophilic dye is described in Japanese Patent Application (OPI) No. 58543/83 (the term "OPI" as used herein refers to a "published unexamined Japanese patent application"). According to this method, a light-sensitive material containing a silver halide and a dye providing substance which acts as a reducing agent to silver halide at a high temperature and at the same time which is oxidized itself to release a mobile dye is heated simultaneously with or after imagewise exposure under the condition of being substantially free from water, whereby a mobile dye is formed imagewise.
In such a method of forming an image, a step for forming imagewise a mobile dye by heating and a step for transferring the mobile dye to a dye fixing layer are necessary. It becomes possible to realize a rapid and easy processing if the two steps can be carried out at the same time. From such a viewpoint various investigations had been made, and, as a result, it was found that this can be accomplished with superposing a light-sensitive material and a dye fixing material under the condition of retaining water in the presence of a base or a base precursor which is capable of releasing a base by heating and heating at a temperature lower than the boiling point of a solution (see Japanese Patent Application (OPI) No. 218443/84). Further, with respect to a so-called monosheet type light-sensitive material in which a dye fixing layer is integrated into the light-sensitive material, it was found that this can be achieved by heating under the condition of retaining water by means of coming into intimate contact with a material through which moisture hardly permeates, such as a polyethylene terephthalate film, etc.
However, in the dye images obtained by these methods of forming images bases remain, which may cause problems on health for human body. Therefore, it has been desired to develop a method which can form an image using a base in a concentration as low as possible.
Moreover, it is advantageous in view of saving resources that the amount of silver salt, such as light-sensitive silver halide and organic silver salt, to be employed as a medium for obtaining color images be reduced as much as possible.
From such a point of view, in the field of conventional wet processes using a developing solution or the like, there has been disclosed a method for forming a color image in which a dye image is intensified by means of catalytic function of reduced silver formed imagewise using a so-called intensifying agent. For instance, a method of intensification using a peroxide such as hydrogen peroxide, etc., as an intensifying agent is described in Friedman, History of Color Photography, 2nd Edition, page 406 (1956), West German Patent Application (OLS) Nos. 1,961,029, 2,056,360 and 2,044,993, Japanese Patent Application (OPI) No. 18629/83, etc.; a method using a salt of halogenous acid such as a chlorite, etc., is described in Japanese Patent Application (OPI) Nos. 53826/76 and 13336/77, etc.; and a method using a polyvalent iodine compound such as iodosobenzoic acid, etc., is described in Japanese Patent Application (OPI) No. 73731/82, etc. Among these methods, the method using a peroxide such as hydrogen peroxide, etc., as an intensifying agent is particularly advantageous because it has high amplification efficiency, is free from coloration, and provides harmless reaction products.
It is also known, however, that with respect to the method of forming color images using an intensifying agent, halide ions or various antifogging agents present in a developing solution act as catalyst poison, and reduced silver is poisoned, which results in sever reduction of the amplifying efficiency. In particular, in a case where the intensification processing is carried out using a small amount of solution, the reduction in the amplifying efficiency is considerably large.
Therefore, it is extremely significant from the standpoint of saving resources if dye images having a sufficiently high density can be obtained in a short period of time from a light-sensitive material having a low coating amount of silver using a small amount of solution, preferably water.